One day after getting sued by 15 states, the Environmental Protection Agency (EPA) chief, Scott Pruitt, reversed his decision to delay implementation of Obama-era rules reducing emissions of smog-causing air pollutants.

Pruitt presented the change as his agency being more responsive than past administrations to the needs of state environmental regulators. He made no mention of the legal challenge filed against his prior position in a federal appeals court.

At issue is a 1 October deadline for states to begin meeting 2015 standards for ground-level ozone. Pruitt announced in June he would delay compliance by one year to give his agency more time to study the plan and avoid “interfering with local decisions or impeding economic growth”.

Pruitt, who was Oklahoma’s attorney general prior to his appointment by Donald Trump, has long been an opponent of stricter environmental regulations. Since arriving in Washington, he has repeatedly moved to block or delay regulations opposed by the chemical and fossil-fuel industries.

Wednesday’s sudden reversal was the latest legal setback for Pruitt’s regulatory rollback agenda. Last month, a federal appeals court in Washington ruled that the EPA administrator had overstepped his authority in trying to delay implementation of an Obama administration rule requiring oil and gas companies to monitor and reduce methane leaks.

In a statement issued on Wednesday evening, Pruitt suggested his about-face on ozone standards simply reinforced the EPA’s commitment to working with states through the complex process of meeting the new standards on time.

“Under previous administrations, EPA would often fail to meet designation deadlines, and then wait to be sued by activist groups and others, agreeing in a settlement to set schedules for designation,” said Pruitt, who sued EPA more than a dozen times in his previous job.

“We do not believe in regulation through litigation, and we take deadlines seriously. We also take the statute and the authority it gives us seriously.”

Still, the EPA’s statement said Pruitt may at some point once again use his “delay authority and all other authority legally available” to ensure regulations “are founded on sound policy and the best available information”.

Republicans in Congress are pushing for a broader rewrite of the ozone rules. A House bill approved last month seeks to delay implementation of the 2015 rules at least eight years. The measure has not yet been brought to a vote in the Senate.

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New York’s attorney general, Eric Schneiderman, who led the coalition of states that sued the EPA this week, said the group intended to keep up the legal pressure.

“The EPA’s reversal following our lawsuits is an important win for the health and safety of those 6.7 million New Yorkers, and the over 115 million Americans directly impacted by smog pouring into their communities,” Schneiderman said.

New York was joined in the case by California, Connecticut, Delaware, Illinois, Iowa, Maine, Massachusetts, Minnesota, New Mexico, Oregon, Pennsylvania, Rhode Island, Vermont, Washington and the District of Columbia.

Ground-level ozone is created when common pollutants emitted by cars, power plants, oil refineries, chemical plants and other sources react in the atmosphere to sunlight. The resulting smog can cause serious breathing problems among sensitive groups of people, contributing to thousands of premature deaths each year.